1. Field of the Invention
The invention relates to a control apparatus and a control method for an electric vehicle. More particularly, the invention relates to a control technology that avoids an overvoltage which is caused by reducing the torque of a motor when a vehicle slips.
2. Description of the Related Art
Japanese Patent Application Publication No. 2005-51850 (JP-A-2005-51850) describes a vehicle in which an overcurrent is prevented from flowing in a motor that outputs power to a drive shaft when the vehicle slips. The vehicle includes a boost converter that boosts a voltage output from a battery; and the motor that receives electric power from the boost converter and outputs the power to the drive shaft of the vehicle. In this vehicle, when it is determined that the vehicle is slipping due to idling of drive wheels, the motor is controlled to limit the torque output to the drive shaft. An initial torque value is set based on the degree of torque limitation. When the vehicle has stopped slipping, the motor is controlled to release the torque limitation and increase the torque to the set initial torque value.
In the vehicle, when the motor is controlled to release the torque limitation, the boost converter stably boosts the voltage, regardless of the degree of torque limitation. Thus, electric power can be stably supplied to the motor when the vehicle slips.
However, if the torque output to the drive shaft is rapidly limited when the vehicle slips, the amount of electric power consumed by the motor is sharply reduced. This may cause an overvoltage. The above-described Japanese Patent Application Publication No. 2005-51850 does not describe a preventative measure for an overvoltage.